The invention relates to a method for spinning and crimping a synthetic multifilament yarn, as well as an apparatus for spinning and crimping a synthetic multifilament yarn.
In the production of a crimped yarn, a plurality of strandlike filaments are extruded in a first step from a thermoplastic melt by means of a spin unit. After cooling, the filament bundle is combined and subsequently compressed to a yarn plug by means of a crimping device. In this process, the filaments of the filament bundle are deformed in the yarn plug to loops and coils by means of a preferably heated fluid. To realize such a deformation of the filaments, the crimping device includes a stuffer box chamber, in which the conveying medium compresses the filament bundle to the yarn plug. Thus, the desired loops and coils of the individual filaments form, as the filaments impact upon the yarn plug inside the stuffer box chamber.
To obtain as much as possible a stable crimp, it is preferred to advance the yarn through a heated conveying medium and to heat it at the same time, so that a plastic deformation is able to occur in the individual filaments. To set the crimp, the yarn plug advances through a cooling zone. The cooling zone is formed by a cooling groove preferably on the circumference of a rotating cooling drum. In this arrangement, the length of the cooling zone is defined by the diameter of the cooling drum and by a partial looping on the circumference of the cooling drum. During the cooling, the cooling drum is driven for rotation, so that the circumferential speed of the cooling groove equals the cooling speed of the yarn plug, at which the yarn plug advances through the cooling zone. A method and an apparatus of this type for spinning and crimping a synthetic multifilament yarn are disclosed, for example, in DE 196 13 177 A1.
According to DE 196 13 177 A1, a most effective and uniform cooling of the yarn plug requires a defined duration of the cooling. Thus, the art proposes to increase the dwelling time in that the yarn plug advances with a partial looping over a second, subsequent cooling drum. With that, however, it is not possible to achieve an uninterrupted, uniform cooling of the yarn plug, since the transition from the first cooling drum to the second cooling drum represents each time an undefined interruption of the cooling process.
U.S. Pat. No. 5,974,777 discloses a method and an apparatus for cooling a yarn plug, wherein the yarn plug advances with several loopings over the circumference of a cooling drum. While this procedure permits achieving longer dwelling times for cooling the yarn plug even at higher process speeds, it has the disadvantage that the combined yarn plugs interfere with one another on the circumference of the cooling drum, so that, for example, individual filaments of adjacent plugs interlock and lead to undesired filament breaks upon disentanglement of the plugs. In addition, it is necessary to displace the yarn plugs on the cooling drum surface, so that additional shearing forces act upon the plug. Furthermore, such a displacement on the circumference of the cooling drum may cause individual filaments to interlock on the cooling surface.
It is therefore an object of the invention to further develop a generic type of method and apparatus for spinning and crimping a synthetic multifilament yarn such that after cooling the yarn plug, it is ensured that a stable and high crimp of the yarn is achieved irrespective of the production speed.